Sunday, May 13, 2007

Here is a way to lessen the noise coming into your home or office from the outside - just integrate noise canceling technology into your windows. Tech Digest links to a Discovery News item on just such a technology in development. Sound proofing buildings is a technical challenge, particularly when they are near low frequency noise sources, like airports, rail lines, and highways/motorways. Low frequencies are harder to block as it take a lot of mass to absorb those sounds, compared to high frequency ones.

So, how are Thilo Bein, head of the business unit for energy, environment and health at Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Germany and his team doing it? Their solution is to use piezoelectric materials to vibrate the surface of the window glass so that it destructively interferes (i.e. cancels out) the noises trying to get through the glass, similar to how noise canceling headphones reduce the low frequency sounds on board an aircraft that try to get past the headphones and into the wearer's ears.

This is pretty neat idea which uses the strengths of noise canceling technology (which is good at reducing low frequency noises, but not so good at high frequencies) to solve a problem of our modern, urbanized and mechanized world.

Friday, May 11, 2007

The Headroom website allows you to build a customized graph comparing their measurements from testing many different headphones, including popular and professional over-the-ear, on-the-ear, in-the-ear (earbuds), and noise canceling models. This is a great tool for anyone serious about audio. I highly recommend it.

The Telegraph (UK center-right newspaper) has an article on the unveiling of the Astute, a next generation, British Royal Navy nuclear submarine. Some of the 'factoids' mentioned in the article are very interesting - the nuclear power plant has the acoustic signature of a "torch" (British English for "flashlight"), it can detect the QE2 cruise liner leaving the harbor in New York all the way from the English Channel, and it uses a fiber optic "periscope" instead of the traditional kind. Enjoy!

Wired has an article on Cell Phone ("Mobile Phone" for those unfamiliar with US English) Forensics that comes across as critical in tone, but, in my humble opinion, simply conveys the message that there is nothing magic about cell phone forensics - it is evidence and should be treated as such. That means establishing the chain of custody to preserve it and protect it from intentional and unintentional tampering.

The article makes a point about some software tools not having tamper protection built in. I know that this is a current issue regarding evidence, particularly digital evidence. However, the drive to ideally preserve evidence can be taken too far - real world practicalities must also be acknowledged and accommodated or else the evidential system, and therefore justice, will suffer in the end.

Aside: Please do not mistake my point - I am not against establishing standard operating procedures and best practices for preserving evidence, performing examinations, and the like. What I am against is establishing overly idealistic expectations that are not achievable in the real world across the myriad law enforcement and justice agencies. Put another way, I am for a reasonable balance that is biased toward continually improving the system over time.

The Wired article, at least to my reading, gives the impression that if a tool does not have built-in digital signature protection that it is somehow completely suspect. I don't think that is the case. There are ways to adjust operating procedures to accommodate this, such as MD5 hash generation software routines and proper (in the British sense of the word) evidence handling procedures. I think it is a good idea to have protection built-in, but that it is likewise a bad idea to automatically assume that if a tool that is used in an investigation doesn't have digital signature features built in that the evidence was likely tampered with. That sounds blindingly obvious when approached in this manner, but may not be so obvious to a jury or the general public.

To return to the main thrust of this post, cell phone data is not just any run of the mill evidence, it is "scientific evidence", so someone acting as an examiner needs to recover and analyze the data and then present the results. The article helpfully provides a link to a draft NIST (The National Institute of Standards and Technology, a US government agency) recommendation titled Guidelines on Cell Phone Forensics.

Phone forensics is a helpful tool and can provide valuable clues that would not be otherwise available. But like all scientific evidence, it must be handled, analyzed, and presented properly, and then taken into account along with other evidence, to be of use to investigators and the court.

Thursday, May 03, 2007

OK, I've learned patience over the years, but I'm coming to the end of mine. Since getting my Toshiba Satellite notebook back a week or so ago, I've been noticing an overheating problem. The first time or two I figured that I had blocked the bottom fan grill (speaking of which, is it coincidence that they now call them notebooks instead of laptops? Sitting one on your lap could easily block that grill and these modern processors do get hot.) Anyway, yesterday the fan started making some noise and then stopped. This will be the third time I've had to get this repaired in the approximately nine months I've had it.

Being able to play audio and video files, often years after they were originally created, has been a steadily growing problem for audio, video, and computer forensic examiners.

Of course, video examiners encounter this almost daily if they are dealing with security digital video recorder (DVR) files because of the proprietary codecs (which is short for COder DECoder, and is the software program that converts video to and from a particular digital file format) used by manufacturers of the systems to lock users into their brands.

Even for those who do not process security DVR every day, things have been getting worse. Part of this is due to changes in the latest Windows Media Player where Microsoft removed one of the popular codecs previously used to encode/decode AVI files. Many people are under the impression that AVI is uncompressed and either doesn't need a codec or only has one universal codec. This is far from the truth. AVI, like WAV, is a very flexible format and it supports the use of almost any audio or video codec. To play the file, you have to have the correct codec - period. No codec, no playback - it is that simple.

I was faced with this problem just recently due to the Microsoft changes. The files were uncompressed AVI and would not play on three different machines, even though they played back correctly only two months before. A bit of digging found the cause. The solution ended up being to download an audio/video codec pack. I used the free one found here, but there are others out on the Internet also.

You can imagine how this can be a problem for law enforcement where evidence may need to be archived for up to 25 years and still be able to played back. All it takes is one automatic update and the ability to playback can cease. This is why I recommend to my students that they always include a copy of a freeware player that will play back the media as part of the archived evidence.

Wednesday, May 02, 2007

The Daily Telegraph (UK, center-right newspaper) has an article about a political debate in the UK over whether microphones should be added to CCTV camera installations and whether there should be CCTV cameras that were no obvious displayed or, in other words, hidden.

This has to be a quick posting - unfortunately I don't have time for a fully researched and referenced article, but I'd like to point out a few things from completely different aspects.

The first is from a policy angle. According to the article, the UK has about 4.5 million CCTV cameras. Most of these camera systems are not run by governmental bodies but instead by companies and the like, if I understand things correctly. (It should be noted that the British public supports the use of CCTV)

Adding microphones to CCTV installations brings up the issue of whether non-governmental entities would be allowed to "eavesdrop".

Aside: For purposes of this post, by the term "eavesdrop" I mean listening to conversations which are thought to be private.

Just having a microphone with a camera does not mean that it will be possible to understand individual conversations or even that any collected speech can be listened to or understood by the CCTV operators. For instance, sound captured by microphones can be automatically analyzed (i.e. by a computer) to detect alerting sounds such as gunshots (which are uncommon in most of the UK due to gun control laws), screams or threatening tones of speech. A system could be designed such that the human operator has no access to the audio itself, but is instead only alerted by a text message or other indicator.

To summarize my points from the policy perspective, the act of installing a microphone does not necessarily imply that peoples' conversations are going to be bugged and there are some benefits to be had that do not involve any significant 'invasion of privacy' issues, assuming said system is designed properly. A final policy point is that having private companies collecting conversational speech or installing concealed CCTV in public places raises lots of privacy issues (obviously!). The former seems open to serious abuse unless it is heavily and closely regulated (like the police are). I'm withholding judgment on the latter - there just wasn't enough information in this article for me to form an opinion yet as I don't understand what problem is to be addressed and the perceived benefit.

Although I covered some technical issues while addressing policy, there are a few more points to make from that aspect also. The first is that simply mounting a single omni-directional microphone, no matter how sensitive, up on a pole with a CCTV camera is not going to necessarily pick up conversational speech, as any sound engineer can tell you. What is going to be recorded from way up there by an omni mic during busy times? A cocktail party-like blend of sounds, gunshots, sirens, shouts and other loud sounds is about all that will be heard on the microphone output in real urban scenarios. So, my question is what the microphones are supposed to be for? There are obvious benefits that could be derived, but not without cost and technical implications. It seems to me that there is some need here for some consultations with experts knowledgeable about audio, filtering, and the like before this goes too far.

Anyway, that is all for the moment. Please feel free to comment, but please understand that I wrote this very quickly so I was not able to address all the issues that are raised by the political debate. Nothing is implied by my leaving anything out.

Tuesday, May 01, 2007

The Daily Telegraph (UK, center-right newspaper) has an article on a musical score found encoded on the arches of Rosslyn Chapel (yes, the one from the Dan Brown novel, Freemasonry, et al). What convinced me that this wasn't just another Da Vinci Code styled, publicity-seeking attempt was listening to the motet it transcribed. Why would I have been skeptical? Oh, just that in addition to being found in the chapel associated with the Holy Grail, it also involved Chladni patterns, cubes, and an ex-RAF (Royal Air Force) codebreaker.